1. Field of the Invention
The present invention relates generally to a velocity and concentration adjustable coupling pipe apparatus equipped between a lifting pipe and a collector and, more particularly, to a coupling pipe apparatus which is constructed to, prior to supplying slurry to a lifting pipe, control the velocity and concentration of slurry, thus preventing the slurry containing manganese nodule, fed through a collector when mining the manganese nodule from the ocean floor of the deep sea onto the sea surface, from damaging the lifting pipe or a lifting pump because of a difference in pipe diameter.
2. Description of the Related Art
As the demand for mineral resources increases all over the world, marine mineral resources have been coming into the spotlight as an alternative. Among them, manganese nodule found on the floor of the deep sea has flat or spherical shape and is blackish brown and non-crystalline substances. When collecting the manganese nodule, it is soft. Meanwhile, when the manganese nodule dries, it becomes hardened and thus breaks easily.
The main constituents of manganese nodule are manganese, iron, silica, and water, and the manganese nodule varies in the composition of minor constituents depending on the region. There are several theories about the formation of the manganese nodule, the precipitation of colloidal hydroxides, and the catalysis of iron oxide. The manganese nodule is buried in the deep sea at depths of from 4000 to 5000 m. It is reported that the growth rate of manganese nodule is about 0.01 to 1 mm per every 1000 years.
As shown in FIG. 1, a system for mining the manganese nodule from the floor of the deep sea includes a collector which collects the manganese nodule from the floor of the deep sea, lifting pipes which are coupled to the collector to continuously transfer the manganese nodule onto the sea and comprise flexible pipes, and a lifting pump which provides transfer force to the lifting pipes, and a marine onboard processor which is coupled to an upper lifting pipe coupled to the lifting pump and processes or stores the collected manganese nodule.
However, in the conventional system for mining the manganese nodule from the floor of the deep sea as shown in FIG. 1, the diameters of the lifting pipe and the collector used when mining the manganese nodule may differ as shown in FIG. 2 which is a sectional view illustrating a coupling structure between the lifting pipe and the collector. That is, when the diameter of the lifting pipe is large, the pipe diameter of the collector is small and the lifting pipe and the collector are simply coupled to each other via an expansion pipe, a difference in velocity occurs depending on the size of pipe so that the velocity at the collector increases. According to the law of conservation of mass, the mass passing through the collector must be equal to the mass passing through the lifting system, that is, the lifting pipe and lifting pump. However, a difference in sectional area results in a difference in velocity.
Referring to the following equation, volume flow which is changed into mass flow passing through the pipe must be constant regardless of the diameter of pipe. This is represented by the following equation. largeQ=Qlarge=Qsmall 
Here, Qlarge is the volume flow when passing through a pipe having a larger diameter, and Qsmall is the volume flow when passing through a pipe having a smaller diameter.
The above equation is also expressed as follows.Alargevlarge=Asmallvsmall 
In this equation, Alarge and vlarge are the sectional area and velocity of the pipe having a larger diameter, and Asmall and vsmall are the sectional area and velocity of the pipe having a smaller diameter.
The above equation may also be expressed as follows.
            π      4        ⁢          D      large      2        ⁢          v      large        =            π      4        ⁢          D      small      2        ⁢          v      small      
Here, Dlarge and Dsmall are the diameter of a large pipe and the diameter of a small pipe, respectively.
In this equation, assuming that volume flow is constant, the larger the diameter of the pipe is, the smaller the velocity is. Further, the smaller the diameter of the pipe is, the larger the velocity is. Thus, the equation of vlarge<vsmall is obtained.
Thereby, the velocity of the collector increases, thus negatively affecting stable operation of the collector. A velocity which exceeds a predetermined velocity in a pipe hinders the smooth operation of a pipe wall or the collector.
Particularly, the velocity of particles damages and causes vibration of the pipe wall of the collector. Further, a high velocity increases the velocity of lifting the manganese nodule, thus leading to the damage of the manganese nodule.
Therefore, the velocity of slurry containing the manganese nodule and flowing into the mining system must be constant and must be maintained at a proper velocity or less.
As stated above, in order to stably operate the lifting pump, a predetermined flow rate must be maintained; however, if the diameter of the collector is different from that of the lifting pipe constituting the lifting system, a proper amount of slurry which is the mixture of manganese nodule, seawater and mud does not flow into the lifting system (lifting pipe+lifting pump). In this case, negative pressure is applied to the lifting pipe which is a flexible pipe which couples the lifting pump to the collector. This causes the deformation of the lifting pipe which is the flexible pipe, as shown in FIGS. 3A and 3B, thus blocking the lifting pipe and reducing a flow rate. This causes a larger negative pressure to be applied to the lifting pipe. In order to overcome the problem, the elastic modulus of the lifting pipe which is used must be increased to resist the negative pressure. However, this lowers the elasticity of the lifting pipe which is the flexible pipe, thus hindering the entire system from being smoothly operated at the time of lifting.
Therefore, in order to solve the above problem, a proper amount must be flow into the lifting system. However, it is impossible for the simple expansion pipe of FIG. 2 to realize the inflow of the proper amount.
Further, it is necessary to control the concentration of slurry flowing into the lifting system. As the volume of manganese nodule increases, it affects the load of a motor of the lifting pump, thus causing the motor to be overloaded. In order to prevent the motor from overloading, it is required to appropriately control the concentration of the slurry fed into the collector.
The lifting pump is designed to transfer slurry containing a certain amount of manganese nodule as well as mud. If the concentration of the slurry is high, mass which is to be transferred by the lifting pump is increased and thus the load acting on the motor is increased. Thus, the concentration of slurry fed into the lifting pump, that is, slurry containing seawater, manganese nodule and mud of the ocean floor must be kept constant. In order to achieve it, the following equation is used. Solids Out
The concentration Scon of slurry is as follows:
      S    con    =      100    ⁢    s    ⁢                  Solids        ⁢                                  ⁢        Out                              Liquid          ⁢                                          ⁢          Out                +                  Solids          ⁢                                          ⁢          Out                      ⁢          (              wt        .                                  ⁢        %            )      
In this equation, Scon is the concentration of slurry and Solids Out is the volume flow of manganese nodule which is discharged or introduced, and Liquid Out is the volume flow of seawater which is discharged or introduced.
Thus, when Solids Out increases, Liquid Out must be increased so as to keep Scon constant. Therefore, the inflow of seawater into the lifting pump must be increased. Consequently, by keeping the concentration of slurry flowing into the lifting pump constant, load applied to the motor of the lifting pump can be kept constant.
Further, there is a case where an increase in the inflow amount of seawater is required. That is, when the lifting system is temporarily blocked because of the inflow of an excess of manganese nodule, the inflow of seawater needs to be increased in comparison with the inflow of manganese nodule so as to prevent temporary blocking. Thus, a system for increasing only the amount of seawater is required.
That is, when an excessive amount of manganese nodule enter the lifting system having the lifting pump and the lifting pipe, an impeller or a discharge casing of the lifting pump may be blocked. In order to solve the problem, the concentration of manganese nodule must be kept constant. However, the simple expansion pipe of FIG. 2 or the lifting system which does not consider the inflow of external seawater cannot avoid the above-mentioned problem. Thus, when an amount of manganese nodule exceeding a predetermined amount flows into the collector, a predetermined amount of seawater must be additionally fed into the lifting system so as to control the concentration of manganese nodule fed into the lifting system.
Further, when the lifting system and the collector are operated for a predetermined period of time and then stop operating, manganese nodule or residual materials of mud may be caught between the impeller and an impeller casing surrounding the impeller in the lifting pump. This restrains operation of the impeller, so that the impeller does not rotate and thus the motor may burn out. In order to solve such a serious problem, the inflow of only seawater into the lifting system is required without slurry after the operation so as to remove remaining slurry and remove slurry from the lifting system for a subsequently occurring operation.